Disk storage devices having controller interfaces such as Small Computer System Interface (SCSI), Integrated Drive Electronics (IDE), also known as Advanced Technology Attachment (ATA), Advanced Technology Attachment Packet Interface (ATAPI) etc., are typically used by a personal computer (PC) as storage. The PC serves as a host computer to the disk storage devices. Such a disk storage device includes various electronic circuits including, for example, a device processor for controlling the operation of the disk storage device in response to commands from a host processor which effects control of the PC. One of the control functions performed by the device processor and the electronic circuits in the disk storage device is to improve the performance of the disk storage device by optimizing the execution of plural commands requesting access to plural data storage locations on the disk. Optimizing the execution of plural commands attempts to reduce a service time for executing the plural commands. The service time can be reduced, for example, by reordering the sequence of execution of the plural commands. Reordering the sequence of the execution of the plural commands affects factors such as seek time, rotation time and other factors with respect to each command.
Seek time is the time required for the read/write head to move across the disk to a predetermined position where the desired data storage location can be accessed by the read/write head. Rotation time is the time required for the disk to rotate to a point where the desired data storage location can be accessed by the read/write head.
Accordingly, the optimization operation reduces the service time of the plural commands by reordering the sequence of execution of the plural commands affecting the seek time, rotation time and/or any other factors with respect to each of the commands.
Having the above-described optimization operation performed by the device processor and the electronic circuits in the disk storage device has various disadvantages. For example, inclusion of the device processor and the electronic circuits can cause the disk storage device to be complex. Also, in order to perform other more sophisticated optimizing operations or to modify or add to the existing optimizing operation, the device processor may require re-programming, which can be difficult under normal circumstances, and additional electronic circuits may be required. Further, the device processor in such a disk storage device performs many functions the host processor can perform. Still further, the inclusion of the device processor and the electronic circuits in the disk storage device adds additional costs to the disk storage device, thereby increasing the price of the host computer.
Even beyond the above, ATA type disk storage devices do not support the storage and eventual execution of multiple outstanding commands requesting access to the disk storage device, since no queue for storing the commands is provided in the disk storage device. Thus, the above described optimization where the service time of plural commands is reduced by reordering the sequence of execution of the plural commands cannot be conducted.